1. The Field of the Invention
The present invention relates to gingival retraction cords. More particularly, the present invention relates to chemically impregnated knitted retraction cords having high resistance to degradation and good absorption.
2. The Related Technology
When performing various dental procedures, it is often desirable to retract the gingival tissue to prepare the patient's teeth for the procedure. Taking dental impressions, placing crowns, performing bridge work, or effecting other dental restorations are examples of procedures that benefit from retracted gingival tissue. A widely used method for retracting gingival tissue involves the use of retraction cords which are typically braided or knitted for increased strength, flexibility and resilience. Examples of braided or knitted gingival retraction cords may be found in U.S. Pat. No. 4,321,038 to Porteous, U.S. Pat. No. 4,522,593 to Fischer, U.S. Pat. No. 4,617,950 to Porteous et al., U.S. Pat. No. 4,892,482 to Lococo and U.S. Publication No. 2005/0277087 to Fischer et al., herein incorporated by reference.
The most common purpose for using a retraction cord is to retract the gingiva away from the tooth to take an accurate and reliable impression of the tooth. It is critical to make an accurate impression of the tooth when constructing artificial crowns to ensure that the crown remains properly secured to the tooth for an extended period of time. It is particularly important to make an accurate impression of the tooth in the area at or below the gingival margin. Failure to take an accurate impression can result in a poorly-formed or deficient prosthesis, particularly at the gingival margin. Premature failure of a crown is often due to poor marginal detail in the impression used to fabricate the crown.
The person's gingiva, or “gums”, not only prevents an accurate impression of the proper shape of a person's tooth beneath the gingiva, it may also bleed if torn or damaged by high speed cutting drills or burrs used to remove tooth material preparatory to placing a crown. This bleeding may further interfere with the taking of a good impression because extravasated blood tends to prevent adequate cleaning and drying of the marginal area of the tooth prior to taking an impression and tends to displace the impression material before it can set. Thus, the dual problems of contraction of the gingival cuff and the presence of hemorrhaging tissues make it impractical to simply take an impression following shaping of the tooth with a high speed drill or burr without retraction of the gingiva.
To control or inhibit the tendency of the gingiva to bleed when physically retracted by the retraction cord and/or if accidentally cut or nicked by the high speed drill or burr, retraction cords are often treated with a hemostatic agent. One type of hemostatic agent includes astringents, which lock or seal off exposed blood vessels so as to arrest bleeding. U.S. Pat. Nos. 4,321,038, 4,522, 593, 4,617,950 and 4,892,482, referred to above, discuss the use of astringents such as potassium aluminum sulfate, also known as “alum”.
Many chemicals used to impregnate a retraction cord can have an adverse affect on the strength and integrity of the fibers in the retraction cord. Many retraction cords are made of knitted or braided cotton fibers, which are absorbent so as to retain the active agent within the cotton fibers. However, the use of a hemostatic agent in the retraction cord can degrade the cord over time, making it more likely to fray and/or fail during use. If fibers in the knit or braid fail during use, the dental packing instrument used to insert the retraction cord into the sulcus can slip through the fibers and potentially cut or injure the underlying tissue. In addition, fragments of the retraction cord can remain embedded between the tooth and gums, providing greater risk of infection. Frayed filaments can easily lodge within coagulum, which can be painful to the patient and result in a recurrence of bleeding when the cord is removed. Furthermore, the expandability and resilience of the retraction cord diminishes as the integrity of the knit or weave of the cord degrades.
Therefore, it would be an improvement in the art to provide a gingival retraction cord that is absorbent so as to retain an active agent (e.g., a hemostat solution), and which also resists decomposition and degradation due to a hemostatic or other corrosive agent. It would be a further improvement if such a retraction cord could be formed from strands comprising a single material while maintaining desired properties of being absorbent yet resistant to corrosive dental materials.